A hybrid electric vehicle (HEV) is a vehicle which combines a conventional propulsion system with an on-board rechargeable energy storage system to achieve better fuel economy and cleaner emissions than a conventional vehicle. In a parallel configuration (not shown), an HEV will commonly use an internal combustion engine and batteries or ultracapacitors to power electric propulsion, however the ICE will also provide mechanical power to the drive wheels.
Referring to FIG. 22, in a series configuration, an HEV drive system 2200 will commonly use an energy source such as an internal combustion engine (ICE) 2210 and a pack 2220 of batteries or ultracapacitors to provide electric propulsion power to the drive wheel assembly 2230. In particular, the ICE 2210 will be coupled to a generator 2212, which will generate electricity to power one or more electric propulsion motor(s) 2232 and/or charge the energy storage 2220. Also, multiple electric propulsion motor(s) 2232 may also be mechanically coupled via a combining gearbox 2236. Propulsion motor(s) 2232 for heavy duty vehicles (i.e., having a gross weight of over 10,000) may include two AC induction motors that produce 50-150 kW of power (×2) and having a rated DC voltage of 650 VDC. Due to the high temperatures generated, high power electronic components such as the generator 2212 and electric propulsion motor(s) 2232 will typically be cooled (e.g., water-glycol cooled), and may be included in the same cooling loop as the ICE 2210. Additionally, since the ICE's 2210 primary function here is simply to drive the electric generator, the ICE 2210 may be optimized for limited range of operation and can run more efficiently than a conventional ICE, which must be designed to provide drive power over various speed and loading profiles.
As an added feature, rather than dissipating kinetic energy via friction braking, many HEVs recapture the kinetic energy of the vehicle. In particular, kinetic energy is recaptured via regenerative braking, wherein the electric propulsion motor(s) 2232 are switched to operate as generators, and a torque is applied to the drive wheel assembly 2230. This torque results in a net braking force on the vehicle. As the vehicle slows, it transfers its kinetic energy to the motor(s) 2232, now operating as a generator(s), and electricity is generated. The electricity generated is then stored in the energy storage 2220 to be used later in the drive cycle. Regenerative braking may also incorporated into an all-electric vehicle thereby providing a source of electricity generation onboard the vehicle.
When the energy storage 2220 reaches a predetermined capacity (e.g., fully charged), the HEV may then dissipate any additional regenerated electricity through a resistive braking resistor 2240. Typically, the braking resistor 2240 will also be included in the cooling loop of the ICE 2210. By recapturing its own kinetic energy, the demand on the ICE 2210 to generate energy is also reduced, thus making the HEV drive system 2200 even more efficient.
An HEV drive system 2200 may include multiple energy sources. Examples of typical HEV energy sources include: an engine 2210 (e.g., ICE, fuel cell, CNG, etc.) mechanically coupled to a generator 2212, an energy storage device 2220 (e.g., battery, ultracapacitor, flywheel, etc.), and a reconfigurable electric propulsion motor 2232 mechanically coupled to the drive wheel assembly 2230. These energy sources may then be electrically coupled to a buss, in particular a DC high power buss 2250. In this way, energy can be transferred between components of the high power hybrid drive system as needed.
An HEV may further include both AC and DC high power systems. For example, the drive system 2200 may generate and run on high power AC, but convert it to DC for storage and/or transfer between components across the DC high power buss 2250. Accordingly, the current may be converted via an inverter/rectifier 2214, 2234 or other suitable device (hereinafter “inverters”). Inverters 2214, 2234 for heavy duty vehicles (i.e., having a gross weight of over 10,000) may include a high frequency IGBT multiple phase water-glycol cooled inverter with a rated DC voltage of 650 VDC having a peak current of 300 A. As illustrated, HEV drive system 2200 includes a first inverter 2214 interspersed between the generator 2212 and the DC high power buss 2250, and a second inverter 2234 interspersed between the generator 2232 and the DC high power buss 2250. Here the inverters 2214, 2234 are shown as separate devices, however it is understood that their functionality can be incorporated into a single unit.
In addition to utilizing different type electrical currents, not all energy sources of drive system 2200 provide an identical and/or static energy profile. For example, energy storage 2220, comprising a bank of ultracapacitors in series, may have an initial DC voltage of 700 VDC, however, its voltage decreases significantly as it discharges, proportionally to its static charge. Propulsion motor(s) 2232 for heavy duty vehicles may require an operational voltage on the order of 650 VDC or more. Accordingly, in order to provide sufficient operating voltage when the energy storage is discharging, it may be desirable to substantially step up the voltage of the energy storage from an available voltage to an operational voltage.
One technique for efficiently increasing the voltage of the electricity available on the DC buss 2250 involves using an inductor-based boost converter, DC-DC converter, or chopper (hereinafter “DC-DC converter”). See for example, J. W. McKeever, S. C. Nelson, and G. J. Su, “Boost Converters for Gas Electric and Fuel Cell Hybrid Electric Vehicles,” Oak Ridge National Laboratory, ORNL/TM-2005/60, May 27, 2005. With a high power electric drive system, such as found in metropolitan transit buses, trolley cars, refuse collection trucks, and other heavy duty vehicles, the DC-DC converter may see DC currents on the order of 300 A at 800 VDC.
Unlike much lower rated circuits and systems, a heavy duty HEV/EV will require a high power inductor specially adapted for both the much higher loading and the unique mobile environment of a heavy duty vehicle (e.g., heat, vibration, environmental exposure, high reliability, etc). More importantly, at these ratings, heat becomes a major factor in the device's performance. Toroid-type high power inductors have been used with some success in this application, wherein the inductor casing is mated to a heat sink, to improve the inductor's performance. Toroidal inductors can have higher Q factors and higher inductance than similarly constructed solenoid coils. However, under the conditions of a heavy duty HEV/EV, the dissipation of heat is a limiting factor of an inductor's/inductor-based high power component's performance.
As the demand for HEVs and EVs increase, consumer demand for vehicle performance will also increase. Consumers will require greater performance and greater efficiency. With regard to DC-DC converters on HEVs and EVs, increased performance is associated with larger components; however it is desirable that large, bulky components on the vehicle, such as the heavy duty inductor become smaller and more lightweight. In addition, consumers will desire maximum performance at minimum cost. The invention seeks to address the abovementioned problems.